With the evolution of more complex infrastructures requiring enhancement, re-placement, and expansion in all areas of human occupation, and in particular high-density areas such as cities and suburbs, the ability to accurately map the location of buried conduits, wires and pipelines of various sizes and kinds becomes more pressing, as does the need to document actual as-built underground installations before they are covered so that they can be precisely located at a later date.
Worker safety and project economic concerns also require the location and identi-fication of existing underground utilities such as underground power lines, gas lines, phone lines, fiber optic cable conduits, cable television (CATV) cables, sprinkler control wiring, water pipes, sewer pipes, etc., collectively and individually herein referred to as “buried objects.”
The unintended destruction of power and data cables may seriously disrupt the comfort and convenience of residents and bring huge financial costs to business. Therefore human-portable buried object locators (also denoted herein for brevity as “locators”) have been developed that sense electromagnetic signals to locate buried utilities such as pipes and cables. Buried objects are frequently located by utility employees or other uses by moving a locator over the ground or other surface and receiving and processing electromagnetic signals emitted from the buried objects. These operations are also known as “line tracing” or “locates.” If the buried conductors carry their own electrical signal, they can be traced by detecting the emitted signals at their corresponding frequency or frequencies, such as 50 or 60 Hz or harmonics thereof for underground power cables. Signals with a known frequency may also be applied to pipes and cables via a transmitter and either directly or inductively or capacitively coupled to enhance the ease and accuracy of the line tracing. During these operations, also known as “locates,” it is desirable to track the position and location of the locator or other device throughout its movement.
Portable utility locators typically carry one or more antennas that are used to detect the electromagnetic signals emitted by buried pipes and cables, and by sondes that have been inserted into pipes. The accuracy of portable utility locators is limited by the sensitivity and the configuration of their antennas. Moreover, precise locating of the position of a locator on the surface of the earth—as would be needed, for example, in order to build an accurate digital map of the locating results—has been problematic because of imprecise positioning technology and an inability to track the position of a locator relative to the ground itself.
Accordingly, there is a need in the art to address the above-described as well as other tracking related problems.